1. Field of the Invention
The present invention relates to a roller bush for a fuel injection pump.
2. Description of the Related Art
Japanese Unexamined Utility Model Publication No. 63-151967 discloses a fuel injection pump having a cam reciprocating a plunger, a metal roller forced into contact with the cam, a pin supporting the roller rotatably about a rotational axis, and a bush interposed between the roller and the pin, the pin being supported at both axial sides of the bush. In the fuel injection pump, the bush comprises a metal having ceramic coatings covering the inner and outer surfaces. Namely, the ceramics coatings are interposed between the bush and the roller, and between the bush and the pin, which slide to each other, respectively, to suppress the seizure and the wear of the bush, the roller, and the pin, to thereby ensure the durability of the fuel injection pump as much as possible. Further, the ceramic is used in the form of a coating. This reduces the amount of the ceramic used, and thereby reduces the production cost of the fuel injection pump as much as possible.
However, the adhesion between a metal and a ceramic is generally low, and the relatively large force acting on the bush may separate the ceramic coatings therefrom. Especially, when the pin is supported at both axial sides of the bush, as mentioned above, a bend will occur at the center of the pin due to the force on the roller by the cam, and thereby a large force will act on the axial end portions of the roller and the bush. Such a large force may lead to the separation of the ceramic coatings and seizure, and thus the durability of the fuel injection pump may deteriorate.